Cairn Terriers fighting

We have a 7 year old & a 4 year old Cairn Terriers. The 4 year old is very aggressive. She has attacked the 7 year old several times. They have both drawn blood & had to go to the vet for infections. We do not want to have to get rid of either dog, but cannot let the 4 year old attack the 7 year old any longer. Thanks is advance for your help.

Be sure to hide toys, bones, food and other possible possessions. This will allow the dog to simply get to know each other without having to argue. Gain knowledge about dog body language and watch for signs of arousal. A stiff body with an erect head and tail wagging slowly in a tight fashion are meant to be warning signs. Other signs include a hard stare, hackles up, leaning forward up on toes, and lips tightening with widening eyes. This is the time to calmly and quietly remove your dog from the situation. Never wait to see what’s going to happen. You can also hire a personal trainer for your 4-year old dog to avoid fights since he's the one initiating.

The Dog Line offered great suggestions, I just want to stress that this problem can not be handled online. You need a hands on positive trainer to help you. Terriers are known to be scrappy with other dogs, it's part of their breed instincts. Best of luck~